Fast Sorting Algorithms on Uniform Ladders (Multiple Shift-Register Loops)

This paper presents two sorting algorithms on the uniform ladder (a new storage device based on charged coupled devices, or magnetic bubbles implementation, proposed by Chen et al.). It is assumed that control and comparison timings are negligible when compared to the relatively slow bubble movements. The first algorithm (Algorithm 1) enables the sorting process on a single ladder to be completely embedded in the input/output time (whereas Chen´s algorithm (SLISO) has a 20 percent unoverlapped sorting time in the load-sort-unload process). When one ladder cannot accommodate all the input records and two or more ladders are needed, Algorithm 2 attains a negligible unoverlapped sorting time (which can be removed with a minor modification in the system hardware and hence in Algorithm 2). In comparison, Algorithm 2 obviates the need for explicit merging of the ladders, which is required in Chen´s algorithm (MLISO). This implies that unlike the MLISO scheme, ladders are not tied up for merging, and can be recycled once their contents are outputted. Therefore, in a real processing environment, the number of ladders required by Algorithm 2 may even be less than the theoretical minimum which can be attained by the MLISO scheme.